div.主框架{
    background-color: #eef2f6;
    width: 360px ;
    height: 640px ;
    border: 1px solid black;
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%,-50%);

}

a{
    text-decoration: none;
    color: white;
}

button.返回{
    margin-left: 20px;
    margin-top: 20px;
}

h1{
    text-align: center;
    margin-top: 100px;
    color: red;
}

h2{
    text-align: center;
}

select.选择年级{
    width: 320px;
    height: 30px;
    text-align:center;
    display:block;
    margin-left:auto;
    margin-right:auto;
    margin-top: 50px;
}

input.请输入你的手机号{
    width: 320px;
    height: 30px;
    text-align:center;
    display:block;
    margin-left:auto;
    margin-right:auto;
    margin-top: 10px;
}

button.获取验证码{
    width: 270px;
    height: 35px;
    display:block;
    margin-left:auto;
    margin-right:auto;
    margin-top: 10px;
}

button.快捷注册{
    width: 270px;
    height: 35px;
    display:block;
    margin-left:auto;
    margin-right:auto;
    margin-top: 10px;
}